You can't say it is not true, when studies have proven that almost the majority of intelligent people at young age struggle with this problem if they are not getting enough "attention" / challenges (if you know what I mean) in the early years of their life. Its really common for people with above average intelligence to under perform (especially early life) because of so many reasons, the one I stated is just one of them.
Yes lots of people are good in high school but have difficulties in uni, and there can be many reasons for that. If you always study hard in high school, get good grades but spend a lot more time on each subjects as "normal" then yes, uni will be a lot harder for you. Or perhaps the topics in uni don't interests you anymore, can be anything.
All I am saying that it can also work the other way around, that the fact that people can't finish their uni or whatever isn't always because they aren't capable (well, they aren't in a literal sense since they didn't make it) but its not because they are not intelligent enough. I finished it, that is not the problem.
You don't want to know how many issues I had because of anxiety, no motivation, at some point, not even motivation to live my life. I talked with many professionals about it, even had to do multiple intelligence tests, they spoke with my parents about my early life to figure out what might have caused my despair. More intelligent people are also a lot more vulnerable for depression.
Since then I read a lot about philosophy, psychology and especially topics such as autism, bipolar, depression, causes of them etc interest me. If I can from both personal experience and other studies and research conclude that many of "intelligent people" first don't even realize it themselves and often think they are weird, and struggle with many basic tasks because of it it just feels bad man.
That is why I said what I said, because I am afraid that a lot of very intelligent and capable people will bring themselves down because of so many reasons, isolation, not able to relate, thinking of a different level, seeing though people their intentions, struggling with justice, always asking why, and wondering what is the point of doing something etc.
What OP said could be one symptom of him clearly being more intelligent than those around him, and my post was to hopefully make him aware of that possibility earlier then I thought about it. So he can prepare himself properly, or do the required tests, and than seek the necessary help to make sure his intelligence does not goes to waste.
TLDR: It is common, from what I can see and experience, I want to make OP aware of this, so he can improve himself.